Inkjet printing is a method of printing that is well known in the art. The basics principles of this technology are described, for example, by Jerome L. Johnson in “Principles of Nonimpact Printing”, Palatino Press, 1992, Pages 302-336 (ISBN 0-9618005-2-6). Commercial products which use inkjet printing methodologies are widely available, including computer printers and large format graphics printers.
An ink-jet print head typically consists of an array or matrix of ink nozzles, wherein each nozzle is adapted to selectively eject ink droplets. A given nozzle of the print head ejects an ink droplet in a predefined print position on the media. Thus, by adapting the nozzle(s) to move relative to the media, and by ejecting ink droplets in a particular arrangement or pattern on the media, a desired pattern or image may be printed.
Recently, curing of ink by radiation and in particular ultraviolet (UV) radiation has become popular in the field of printing. In such cases, the printer is equipped with a source of curing radiation such as a UV lamp or UV Light Emitting Diodes (LEDs) and special radiation-curable ink is used. An image printed by such a printer may then be cured by exposure to the curing radiation. “Curing” in the context of the present disclosure means a process of converting a liquid such as a monomer and in particular ink to a solid, by exposure to radiation, which may be UV radiation.
To obtain adequate curing of the curable ink, it must be exposed to UV radiation of sufficient power. Otherwise, uneven ink curing may take place. For example, if the radiation does not penetrate through the whole ink layer, a lower portion of the ink layer will not be cured, thereby leaving reactive monomers in the printed area, and interfering with the adhesion of the ink to the media substrate.
UV radiation/light may be generated by expensive mercury-containing lamps, which consume large amounts of energy, most of which is converted into heat. Such lamps quickly deteriorate with the time, and therefore need to be replaced regularly.
Preferably, prints should be ready for use at the end of the printing process, meaning that the printed ink should be fully cured. As the printing speed increases, the power of the UV lamps required to ensure complete ink curing to must also increase. Unfortunately, the life time of high power lamps is shorter than lower power lamps. Furthermore, the cost of high power lamps is generally disproportionately higher than lower power lamps. Thus, the UV lamps have become a speed-limiting factor for inkjet printing processes that use curable ink.
Consequently, there remains a need to develop a printing method that will enable high-speed printing and curing with reduced UV radiation power requirements.
Like reference characters refer to the like parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.